Jeremy Scahill’s Dirty Wars is a great read. It asks how a policy of assassination relates to the way America is governed and the way it interacts with the world. At its best, the book asks vital questions about the scope and parameters of America’s use of force. It probes the largely unchecked programme of extrajudicial killings that Barack Obama has embraced. Scahill indicts the dark geopolitics of Washington (shared by members of both parties), with which America, through its imperial president, wages an ever-expanding war. Dirty Wars is an in-depth study of the US’s war against Islamists before and since 9/11, of Washington’s remapping of the whole world as its battlefield and of the assassination programme carried out by an arsenal of drones, special forces and mercenaries. Alas, Dirty Wars is also a mixed bag of a book. Too often it degenerates into unbalanced polemic. At critical points in the story, Scahill misses opportunities to deliver a serious analysis of the superpower’s use of force.